Filament mount for high-power tubes



June 6,1950 'J. w. CLARK 2,510,171

FILAMENT MOUNT FOR HIGH POWER TUBES Filed May 25, 1948 2 sheets-sheet 1FIG. I. r ||||||||Hl Jo HIV W CLARK lhwentor Gttorueg June 6, 1950 J. w.CLARK 2,510,171

FILAMENT MOUNT FOR HIGH POWER TUBES Filed May 25. 1948 2 sheds-s58 2Patented June 6, 1950 FILAMENT MOUNT FOR HIGH-POWER TUBES John W. Clark,Cedar Rapids, Iowa, assignor to,

Collins Radio Company, Cedar Rapids, Iowa, a corporation of IowaApplication May 25, 1948, Serial No. 28,984

13 Claims.

This invention relates to high power electron tubes, and more especiallyit relates to thermionic filament units or mounts for such tubes.

A principal object of the invention is to provide a more efiicientthermionic filament mount for high power electron tubes.

Another object isto provide an improved multisection filament and mountfor high power tubes, wherein filament bowing is reduced to a minimum.

Another object is to provide a filament mount of the basket type,wherein the filament strips or sections are mounted so as to preservetheir proper spaced relation with respect to an associated grid, whilepermitting each strip or section to elongate without bowing.

Another object is to provide a filament mount of the baskettype,,wherein the efiects of end cooling are reduced to a A feature ofthe invention relates to an improved high power thermionic filamentmount, wherein the filament strips are supported in parallellongitudinal array and equi-distant around a common .center forcooperation with a surrounding grid.

Another feature relates to an improved high power thermionic filamentmount, wherein the filament strips are supported in radialandsubstantially planar array with respect to a common center forcooperation with a corresponding planar grid.

Another feature relates to an improved thermionic filament and mountwhich is particularly useful in high power ultra-high-frequency tubes,wherein the electron transit time between the filament and control gridmust be accurately determined with respect to the operating frequencyof. the tube. An example of such a tube is the so-called Resnatron, asdisclosed for example in U. S. Patent No. 2,405,763.

A still further feature relates to the novel organization, arrangementand relative location of parts which cooperate to provide an improvedfilament mount for high power electron tubes, particularly those of theultra-high-frequency type.

Other features andadvantages not particularly enumerated, will beapparent after a consideration of the following detailed descriptionsand the appended claims.

In the drawing:

Fig. l is a generalized view, partly perspective and partly sectional,of a filament mount embodying certain features of the invention.

Fig. 2 is a vertical sectional view of one filament mount structureaccording to the invention.

Fig. 3 is a top plan view of Fig. 2.

Fig. 4 is a bottom plan view of Fig. 2.

Fig. 5 is a vertical sectional view of a modified. filament mountaccording to the invention.

Fig. 6 is a top plan View of Fig. 5.

Fig. 7 shows the general method of supporting the mount of Figs. 2 and 3within a tube envelope or housing.

Fig. 8 shows the general arrangement for supporting the filament mountof Fig. 5 Within an evacuated tube or housing.

In certain kinds of high power ultra-high-frequency electron tubes, ofwhich the so-called "Resnatron is typical, the factor of electrontransit time between the cathode and control grid is of greatimportance. For example in the Resnatron, the useful emission whichreaches the anode is dependent upon a space charge layer adjacent thecathode which is of sufiicient thinness so as not materially to increasethe transit time of an electron in its trajectory between the cathodeand the control grid. However, in order to achieve the best results withthat type of tube, not only must'the filament be capable of supplyinglarge quantities of electrons, but it must also preserve a uniform spacerelation with respect to the adjacent grid, even at the very hightemperatures at which the filament operates- Furthermore, it is highlyimportant that the temperature at each point of the filament strip be asuniform as possible. Because of the necessity of providing relativelymassive anchoring rings or supports for the multi-strip filament, theproblem of end cooling is of much greater importance inultra-high-frequency power tubes than it is in conventional tubes to beused at relatively low frequencies. The filament supports for suchultra-high-frequency high power tubes must therefore perform threeseparate functions. They must support the filament in the proper spatialrelation to the grid; they must permit the filament strip to elongatewhen hot, to minimize bowing; and they must cause no substantial endcooling. I have found that these three objectives can be realized byappropriate design of the supports and by appropriate choice ofmaterials, dimensions andshapes for the various components of the mountasa whole.

In the filament mount according to the invention, the filament consistsof a series of linear parallel strips arranged in a circular arrayaround a common center so as to cooperate with an adjacent grid. Thesupport for-such a mount therelugs, but a radialdisplacement tendsmerely to stretch the lugs without.afiectin there uired rigidity of thefilament support.

Such an arrangement is shown in generalized form in Fig. 1, comprising athin-walled metal, tube 1, for example of nickel, which at its lower 7end is welded or otherwise rigidly vfastenedto a: copper ring 2. Theupper end of tube I is bent at right angles to form the desired.numberof integral and radially extending'lugs 3." Welded 1 to the endsof lugs 3 are respective tabs 4 of a refractory metal such as tantalum.Vertically beneath the ring 2 and rigidly supported" in spaced relationthereto is another copperringgi which has welded or otherwise fastenedthereto another thin-walledmetal.tube: 6 whose upper end is bentatrightanglestoform integralradial lugs T'equal "in number to,landvertically aligned with, the lugs 3. Weldedto the lugs Tare tabs 8of refractory. metal, suchas tantalum. A'nohored'at opposite ends.totheresp'ective tabs 4 0 and 8are the various filament'strips ficoftunigsten or.other similar materialiwhich is conventionall'yfusedlforelectron-emitting cathodes in electron tubes. The filamentstrip's arearranged" to, be heated by. connectingthe terminals of a suitablecurrentsupply respectively to rings 2 and'Sf Byproperdsign o'f'thedimensions and materials for the various elements asidescribed, nosubstantial end cooling?" of the filament strips takes place. Thus whenthe mount isprop- 0 er ly, designed, .if the filament .strips areremoved andthe two endsofthe'iriountare joined together, thehot?"'end.f.of. the'niount would just reach" fila'mentl operating.temperature at' the above integral either numerically or by using apolynomial approximation: for the three functions. In this way by aseries of trials one can find a combination of cross-section and lengthwhich gives the desired temperature drop.

While .Fig... 1-..shows the thin-walled tubular member I having one endbent over at right anglesto forma series of separate radially ex- 'tenolin gglugs this is' not necessary. Thus the thinewalled ,tubularmember Imay be provided with a continuous right-angled flange, and thetabs-4*can-"be-radially attached to this flange at appropriate;circumferentially spaced points.

Referring to Figs. 2 to 4, there is shown one actual construction ormount which has been fdund to possess the desired characteristics. Itcomprises ail'ow'er, ring 9"" of copper or other" metal ofgood"heatfcorrductivity.' Fitted "into-a" recessrin the; upper internalface"of"ring"9*is"a thin-walled 'nickeltubeil ll'fwhichimaybe'welded" toringj. The upperjendoftubel Wisfbent out wardly to forma .rig'htaIIgledfiangeI I. Welded to flange llsoj'asitoextend'fi'radially"outward" therefrom, are the equallyspacedtantalimrtabs I2. The outer end of .each tab [2 may be inth'e" form of aclip '13 to receivethe 'ri'ght angledend I 4 "of the correspondingfilament fstrip I 5 which may be'weldedfto, the tantalum? tabi Thefilament 'stripsare arrang'efso that'th'efl main lengthISTthereofiextnds' parallel: to the axis of ring 9. The upper end;offeach' filament stripislikewise bent"atl"righ't angles and is fas-vtened. or weldedto a corresponding tantalum tab" IS. The tabs l6" arewelded to, and "extend radialratedfil'ament"'current.' Consequentlywhenthe lyoutward from,th.e.fiange lip ITofa thin wall'ed filamentstripsare assenibld'inthe mount, they are suspended'lbetween supports whichare at the same temperature as.thfe filament, and no heat is conductedaway. from the filament ends. Therefore the cross-'secti'onlof the,mount sh be carefully chosen. so .as to. achieve: the desired. result.-The temperature.offthe hot end ofthe filament is determinedjbya .balancebetween the I R'Theat generatedlin the. mount itself; by the: heat"lostthrough' radiationifomithe mount it- 5 self 1 andby, the lieaticon'ductedaway. from the eoolj"'endTof 'the mount. This energy. can be,formulated in 'accordancewith the following in V tegro-difier'entialequation;

The-formal solutionofthisequation is:

where T1 isthe-"temperature of" the hot end and -T thatof the cold end:

When -p; o',- and "r as functionsI-of T areknownt experimentally; on'ecan 'rf hmda 1 proceedto evaluate the" nickel .tube l8 similar to itub'eliiia The tube I8 is rigidly anchored orweldedwith'in a recess I9" inthe lower face of the, upper ,ring member. 20 of copper or the like. ItwiIIb'e understood; that thetabslii are inverticalalignment with thecorresponding tabs IZI If desired, the-strips l5.v ree heu t eir-1rticaldee ihm r Pr e th-@ 61 were v i ell r ieed ne b e asses. o l eat o.1 1;- 3 e se em lateral rigidity. The rings 9 and 2i]haverespecfiver-flan es 1.2.23; wh c extendputwardlvalo t e;hQrizon a;pQrt Qn preach-fi ament s rip.- Q- act;as;electronssl'iieldsjso;'that',: the..e1ectron .emise I sion. fromzthefilament: -.S13EipS1isz;CO11find.-' imgemera-l. to.:,a..rad=ialtrajectory... Thearingsfi. and i.2fl..l

areasuitablyg-fastened tolrespectiverigids'supportsi which-.lmayalso.=.be connectedlato the terminalsof a,suitable'heatingmurrentsupply; Thus; there is shown in Fig. 7,anenclosing evacuatedvessel- Or -housing :24 Extending-through one endof this vesse1is-atubular-metal member :2 fi' 'wh'ich fits over the ring l il and 'can b'e'iastened' thereto by-su itab1e-=screws-'261Likewise, there--is"fitted" into -the' lower 'ring*9 a tubular metalmember-275" The members 25 and 2'! .are connected to re-- spectiveterminalsofasuitab1e"ifi1ament 'current supply source: The filament'mount'is. surrounded. by one" or'more-suita'ble' -grids andjan anode(not shown), so as to complete the electron circuit for thetube.

Referring to Figs; 5" and 61. there. isshown a modification; wherein thefilamentstrips. instead 1 of being in the form ofialtub'ular basket,faremounted in'aradialplanar array. In this'embodimentthere is providedanickel ring. 2 S'formed of thin=walled"metal" stock. Surrounding thestrips 32.

ring 28 and concentric therewith is'another nickel :ring 29 ofthin-walled metal stock. Suitably'attached, for example by welding, tothe vertical rim of ring 28, are a series of tantalum tabs 30.

Likewise welded or otherwise fastened to the vertical rim of ring 29 isa similar series of tantalum tabs 3|, the tabs 39 and 3| being in radialalignment. The filament strips 32 are each in the form of a tungstenstrip having the ends bent downwardly at right angles and welded orotherwise fastened to the ends of the corresponding tabs 39, 3|. For thepurpose of shielding the mount against back emission, there is welded tothe ring 29 on the inner periphery thereof, a

metal bracket 33 to which is fastened an annular metal disc 34 whoseradial length is less than the length of the filament strips 32. Thedisc 34 is provided with a series of parallel upwardly extending channelmembers 35 which extend along, but in parallel spaced relation to, theedges of the associated filament strip. For the purpose of heating thefilament strips, the rings 28 and 29 can be connected to suitablecurrent supply terminals, it being understood that the rings 28 and 29are supported in fixed coaxial relation in any well-known manner. Thusas shown in Fig. 8, the ring 28 is adapted to be fastened to a tubular.member 36, and the ring 29 is adapted to be fastened to a similar outertubular member =3l, the members 36 and 31 being rigidly held in..suitable concentric spaced relation. Associated radially discretefilament support tabs carried bythe rim of one of said members, acorresponding plurality of radially discrete filament support tabscarried by the rim of the other of said members, the tabs on saidmembers being in aligned pairs, and a plurality of filament strands eachstrand being anchored at its opposite ends to a corresponding alignedpair of said tabs, each of said thin-walled metal tubular members havinga predetermined electrical resistance to develop a predeterminedlocalized amount of heat adjacent the filament ends attached thereto inresponse to the filament current flowing therethrough to maintain thesaid filament ends at substantially the same temperature as theremaining portions of the filament.

2. A multi-strand filament mount according to claim 1, in which each ofsaid tabs is an integral extension of the rim of the corresponding oneof said members each of said strands has a main portion extendingparallel to the common axis of said coaxial members, and a pair oflaterally extending portions which are respectively anchored to saidannular members around the periphery thereof.

3. A multi-strand filament mount according to claim 1, in which each ofsaid strands has a main portion extending radially outward from thecommon center of said coaxial members, and a pair having a predeterminedelectrical resistance to ;chored respectively to said coaxial membersaround the periphery thereof.

\4..A multi-strand filament mount for electron tubes, comprising, a pairof coaxial annular filament anchoring members. each in the form ofthin-walled metal tubular stock having its rim bent at substantiallyright angles, a ring of highly conductive metal for each member and towhich .it is :rigidly fastened while permitting said rim to flex withrespect to thering, a plurality of radially discrete filament supporttabs carried by the rim of one of said members, a correspondingplurality of ,radially discrete filament support tabs carried by the rimof the other of said .members, the .tabs on said members being ar- .to acorresponding aligned pair of tabs, each of said thin-Walled metaltubular members having a predetermined electrical resistance to developa predetermined localized amount of heat adjacent the filament endsattached thereto in response to the filament current flowingtherethrough to maintain the said filament ends at substantiallythe sametemperature as the remaining portions of the filament.

.5. AfiIament mount according to claim 4, in which each of said rings isrigid in a radial direction.

6. A multi-strand filament mount for electron tubes, comprising, a pairof spaced coaxial annular filament anchoring members each of thinwalledtubular metal stock, a plurality of radially discrete filament anchoringlugs radially extending from the rim of one of said members, a corretoeach lug, and a filament strand fastened at its opposite ends to acorresponding pair of said clips.

'1. A-multi-strand filament mount for electron tubes, comprising, a pairof spaced coaxial an- .nularfilamentanchoring members each of thin--wal1ed-tubular metal stock, each member having an integral flange, aplurality of radially discrete filament support tabs fastened to theflange on one member, a corresponding plurality of radially discretefilament support tabs fastened to the flange on the other member, and aplurality of filament strands each strand having its opposite endsconnected respectively to a tab on one flange and the corresponding tabon the other flange, each of said thin-walled metal tubular membersdevelop a predetermined localized amount of heat adjacent the filamentends attached thereto in response to the filament current flowingtherethrough to maintain the said filament ends at substantially thesame temperature as the remaining portions of the filament.

8. A multi-strand filament mount, comprising, a pair of axially spacedannular members of thinwalled metal stock, a ring of highly conductivemetal to which one annular member is fastened, another ring of highlyconductive metal to which the other annular member is fastened, and aplurality of filament strands bridged across the rims of said annularmembers to form a basketlike structure, each of said thin-walled annularmembers having a predetermined electrical resistance to develop apredetermined localized amount of heat adjacent the filament ends atorlaterally extending portions which a e an- 7 tached thereto in responseto the filamen stir ice-#104271 :rent :flowing ttherethrough to maintainthes-said filament ends at substantiallysthesame tempera- :ture as the:remaining portions iOf the.'fil-ament, each'ofsaid rims havingattached. theretoaiserie's :of .circumferentially spacedtradially;discrete anchoring tabs to whichthe respective rendsoifsaid ufilamentstrands are connected.

9. A. multi-strand filament mount, comprising, .;a .pair of radiallyspaced "annular members :of thin-walled :metal. stock, v.a radiallyrigid :metal ring to which one of :said members :is fastened, anotherradially rigid .metal ring T110 which ;the other 'of said members :isfastened, each ;of said annular. members having a flange 'lextendingparallel vtofltheir common axis, and a pluralitycof filament stripsbridged :across :said flanges and disposed in radially extending. arrayaround :said common axis,- said :thin-walled .annular'members .having :apredetermined electrical resistance .to "develop a predeterminedlocalizedamountiofheat adjacent the filament ends attached thereto inresponse :to the filament currentflowing therethrough to maintain :thesaid 'filament endsiat substantially the same temperature as theremaining portions of the filament, each of saidv flanges havingattached thereto a series "of circumferentially spaced radially discreteanchoring tabs to which the respective :ends of the said filament stripsare connected.

'10. A multi-strand filament mount for electron tubes, comprising incombination "a pair Of annular metal blocks, a tubular member of"thinwalled metal stock fastened-tonne o'fsaid-blocks, another tubular.member of thin-walled metal stock fastened-to the other block, each ofsaid:

memberShaVing across-sectional thickness which is small in comparisonwith the cross-sectional thickness of the associated block and-having an1 integral flange of small cross-sectional thickness extending-radiallytherefrom, and a plurality of filament strips each being anchored at-.its opposite ends to a respective one of said flanges through theintermediary of --respectiveradially --discrete .lugs attached --'tosaid Lfianges, and each "of said thin-walledmetal tubular'members hav--;

sing :a predetermined electrical resistance which .is low in comparisonwith therelectrical resistanceof the associated block for.-developing apredetermined localized amount-of heat adjacent the filament endsattached tothe blocks in response to filament current flowingtherethrough :and thereby maintaining said filamentends at substantiallythe same temperature-as the re- :mainingportions of thefilament.

-11. A multi-strand filament mount-for electron,

tubes, comprising in combination a paired annular metal blocks ofhighconductivity ,-'a.itubular metal member of thin-walled stock-fastened '=to ione cof sa-id Jblocks; sanotherstubularz metal :mem--ber: of thin-walled :Istock ifastened 'to .the other rblock, eachs-of.saidwmembers having a crossa sectional thickness which is small incomparison -with the cross-sectional thickness of'theasso- .;ciated.;block,'ieach member having anintegral -fiange extending radially:outward therefrom, -:a :.plurality 50f :discretet-filament support tabsin spaced relation around each of :said flanges,;an'd 'azplurality offilament strips. each having :its ioppositeeends :anchored .to ';acorresponding pair 10f said tabs'sand 83011501 said thin-walled tubularzmembers and flanges having :a predetermined electrical resistancewhich. is high in comparison with tthe electrical resistance of theassociated ;block :for developing :a predetermined localized :amount of.heat adjacent :the filament ends stattached-thereto iII'zlSPOllSe to thefilament current :flow to thereby v maintain the said filament ends atsubstantially :the same .temperaturei'as the remaining portions :01 the;filament.

,12. .A multi-strand filament vmount according to claim 11: in whicheach of :said metal blocks .is of copper and 'said'tubular members vareof nickel, said 'tabs being of tantalum and :said .zfilament' stripsbeing of tungsten.

13. "A filament mount for high power radio tubes, comprisingincombinationapair'of'spaced :metal bodies of vgood heat rconductivityand low ielectric-:resistance, a plurality of-yfilament strandssupported at opposite ends from said bodies, and :means interposedbetween each filament end and itspoint of attachment to the associatedmetal "body, the last-mentioned means-being 'ofva mate- ?rial difierentfrom the material of said bodies and having a ,much higher electricalresistance for developing; a predetermined. localized amount of heatadjacent the said points of attachment of the filament strands by reasonof the. filament current flowing therethrough which localized vheatmaintains the filament endsat substantially the same temperature astheremainder of the filament.

Y-JOHN W CLARK.

"REFERENCES CITED The following references r are 1 of record :in thefile of this -;patent:

3 STATES "PATENTS Number Name Date 2,164,477 :Smith :July 4, 1939233851435 "Werner etal. Sept. 25;:194'5 2,405,762 "Sloan Aug. '13, 194623141349 Eite'l 'etal May "11,1948 "245L987 Sloan Oct. "19,1948

""2,4'52,786 ON-eill Nov. 2, 1948

